Transparencies produced from epoxy resins cured with adducts of trimethoxyboroxine and benzyl alcohol and interlayers of mercaptan resins

ABSTRACT

A high heat resistant transparency of epoxy resins cured with adducts of trimethoxyboroxine and benzyl alcohol is disclosed to resist intense heat for these transparencies in their use on military and industrial hardware. This transparency may exist in a composite with other layers of transparent material known to those skilled in the art. The epoxy transparency layer is bound to the other transparent layers, in a variety of configurations, using an interlayer of mercaptan terminated resins. These resins greatly improve resistance to moisture permeability in and about the edges of the entire transparency.

This application is a divisional of my copending application bearingSer. No. 204,424, filed Nov. 6, 1980, now U.S. Pat. No. 4,352,848 for"Transparencies Produced from Epoxy Resins Cured with Adducts ofTrimethoxyboroxine and Benzyl Alcohol and Interlayers of MercaptanResins," which in turn is a continuation-in-part of application Ser. No.070,390 filed on Aug. 28, 1979, now U.S. Pat. No. 4,294,886 which issuedon Oct. 13, 1981.

BACKGROUND ART

Heretofore, the use of transparencies in military and industrialhardware has required exacting properties for their certified use. Forexample, a military helicopter having vast areas of transparent materialwill require special transparent material having identifiable indices ofrefraction to prevent internal reflection of sunlight. Othertransparencies require resistance to penetration by projectiles. Stillother transparencies are designed for resistance to abrasion.

The use of these transparencies in military and industrial applicationshas been severely limited by the temperatures these composite materialscould withstand. Direct application of a heat source or a high energypoint of origin could quickly alter the physical properties of thecomposite materials. Whether the thermal effects be generated by fossilfuel fires or laser application, the conventional transparencies lackedsufficient resistance to the intense heat generated. Therefore, the needexists for a material which is heat resistant, in order to complementthe impact, ballistic, abrasion, or light resistant materials presentlyexisting in composite transparencies.

Likewise, the use of these transparencies in military and industrialapplications has been subjected to irreversible damage caused by thepenetration of moisture into the various layers of the compositetransparent structure. The susceptibility of these materials to moisturepenetration in humid conditions creates a lasting haze within thetransparency structure. Further, the materials must maintain adhesionamong the various layers and also must maintain modulus values among thevarious layers at acceptable and constant levels. Therefore, the needexists for a material which is resistant to moisture permeability toprotect conventional and heat resistant transparent materials from hazecharacteristics but further maintains ultimate strength and constantmodulus.

DISCLOSURE OF INVENTION

Therefore, it is an object of the invention to provide a transparencyproduced from epoxy resins cured with adducts of trimethoxyboroxine andbenzyl alcohol to provide an intense heat resistant material to beincorporated with composite transparencies for use in military andindustrial applications.

It is another object of the invention to provide a transparency producedfrom epoxy resins as above, wherein the intense heat resistant materialhas the same or similar index of refraction in order that it be usedwith other composite materials to complement their properties.

Moreover, it is an object of the invention to provide transparenciesproduced from epoxy resins, as above, wherein the intense heat resistantmaterial may control the reactivity of the entire transparency againstdegradation of properties caused by intense general heat or a highenergized point source.

It is yet another object of the invention to provide a process for theproduction of transparencies having epoxy resins cured with adducts oftrimethoxyboroxine and benzyl alcohol to insure intense heat resistantproperties in the entire transparency.

Still another object of the invention is to provide a transparencyproduced from epoxy resins cured with adducts of trimethoxyboroxine andbenzyl alcohol and triphenyl phosphite to improve the intense heatresistant characteristics of the transparent composite.

Yet another object of the invention is to provide a transparencyproduced from epoxy resins cured with adducts of trimethoxyboroxine andbenzyl alcohol and triphenyl phosphite which can be formed into curvedarticles.

Another object of the invention is to provide a transparency producedfrom epoxy resins resistant to moisture permeability by the applicationof an interlayer binding means within the transparency composite.

Yet another object of the invention is to provide a mercaptan resininterlayer resistant to moisture permeability to protect transparentmaterials from the effects of moisture haze.

Still another object of the invention is to provide a mercaptan resininterlayer resistant to moisture permeability which maintains ultimatestrength and modulus.

Still another object of the invention is to provide mercaptan resin edgesealer resistant to moisture permeability to protect transparentmaterials from the effects of moisture haze.

These, and other objects which will become more apparent as the detaileddescription of the preferred embodiment proceeds, are achieved by: atransparent composition having resistance to intense heat, comprising: atransparent blend having from 80 parts to about 100 parts of an epoxyresin; from 5.0 parts to about 30 parts of trimethoxyboroxine; and from1 part to about 10 parts of a phenyl substituted alkyl alcohol. Theobjects also are achieved by: a transparency composition havingresistance to intense heat, comprising: a transparent blend having from80 parts to about 100 parts of an epoxy resin; from 5.0 parts to about30 parts of trimethoxyboroxine; from 1 part to about 10 parts of aphenyl substituted alkyl alcohol; and from 5 parts to about 25 parts ofa phosphite selected from the group consisting of diphenyl phosphite,trisnonylphenyl phosphite, triphenyl phosphite, diphenylisodecylphosphite, dephenylisooctyl phosphite and phenyldiisodecyl phosphite.

The object of the invention are also achieved by a blend having, (a)about 100 parts by weight of a mercaptan resin having the followingformula: ##STR1## where R is an aliphatic hydrocarbon having from 1 to18 carbon atoms and where n is 1 or 2; (b) from about 40 to about 250parts by weight of an epoxy resin; and (c) from about 0.5 parts byweight to about 4.0 parts by weight of a silane selected from the groupconsisting of:

N-aminoalkyl-aminoalkyl-trialkoxysilanes of the formula ##STR2## whereinR₁ is an alkylene having 1-6 carbon atoms and R₂ is an alkyl having 1-6carbon atoms, and aminoalkyl-trialkoxysilanes of the formula ##STR3##wherein R₁ and R₂ are as defined above and combinations thereof.

The objects of the invention are also achieved by a compositionresistant to moisture permeation, comprising: a transparent blend havinga specific permeability of less than 1.00 mg·mm/24 hr cm² ; said blendcomprising from about 100 parts by weight of a thio-terminated aliphatichydrocarbon based resin; and from about 40 to about 250 parts by weightof an epoxy resin; and from about 0.5 parts by weight to about 4.0 partsby weight of a silane terminated compound.

DESCRIPTION OF THE DRAWINGS

For an understanding of the invention, reference is had to the followingdrawings, wherein:

FIG. 1 is a cross sectional view of the transparency composite havingthe intense heat resistant interlayer;

FIG. 2 is a cross sectional view of the clad transparency compositehaving the intense heat resistant interlayer;

FIG. 3 is a graph of the production of the transparency having benzylalcohol showing the increase in gel time;

FIG. 4 is a graph showing the effect of alcohol levels on the maximumexotherm in the reaction system;

FIG. 5 is a graph showing the increased burn-through resistance on thetransparencies having benzyl alcohol and triphenyl phosphite;

FIG. 6 is a graph showing the increased resistance to moisturepermeability of mercaptan resin binding means bonded to varioustransparency layers when exposed to temperatures of about 200° F. and100 percent relative humidity;

FIG. 7 is a graph showing the increased resistance to moisturepermeability of mercaptan resin binding means bonded to varioustransparency layers when exposed to temperatures of about 120° F. and 95percent relative humidity;

FIG. 8 is a graph showing the increased resistance to moisturepermeability of mercaptan resin binding means bonded to other varioustransparency layers when exposed to temperatures of about 200° F. and100 percent relative humidity;

FIG. 9 is a graph showing the composite evaluation of various interlayerbinding means and the effectiveness of resistance to moisturepermeability;

FIG. 10 is a cross sectional view of a transparency composite at an edgeas sealed by edge sealant material of the present invention;

FIG. 11 is a cross sectional view of a transparency composite having nointerlayer binding means between the intense heat resistant interlayerand the outside ply;

FIG. 12 is an illustrative view of a transparency composite having aslot to be filled and an edge sealant material;

FIG. 13 is a graph showing the variation in concentrations of thecomposition of the present invention and its effect on modulus stabilityduring humidity exposure;

FIG. 14 is a graph showing the variation in concentrations of thecomposition of the present invention and its effect on ultimate strengthstability during humidity exposure.

BEST MODE FOR CARRYING OUT THE INVENTION

Transparencies that have been produced with epoxy resins desiring toachieve heat resistant properties have typically included a boroxinesuch as trimethoxyboroxine. Typical epoxy resins include, but are notlimited to, bisphenol-A type, bisphenol-F type, and novolac type epoxyresins. Typical boroxines include boroxines having the formula ##STR4##where R is a compound having from 1 to 2 to 18 carbon atoms. Desirably,R, is an alkyl compound and has from 1 to 2 to 5 carbon atoms.Trimethoxyboroxine is preferred. Trimethoxyboroxine has exhibited, incombination with epoxy resin, a resistance to heat from a general orpoint source up to temperatures of 2000° F. However, a majorcomplication is the low concentration of trimethoxyboroxine in the epoxyresin system. Previously, for large casting purposes, it was possible touse a concentration of trimethoxyboroxine of 5-7.5 parts per hundredparts of epoxy resin (PHR). Any greater concentration woulddeleteriously promote the reaction between the trimethoxyboroxine andepoxy resin, resulting in a short gel time making it extremelyimpractical to cast large panels.

It has been found that higher concentrations of a boroxine such astrimethoxyboroxine can be incorporated into an expoxy resin system andstill have sufficient time to cast large sheets if a phenyl substitutedalkyl alcohol is added. The alkyl alcohol contains from 1 to 20 carbonatoms and desirably from 1 to 10 carbon atoms. Preferably, Benzylalcohol is used. The alcohol acts as retarder and inhibitor for thetrimethoxyboroxine epoxy reaction, permitting the usage of an increasedconcentration of the trimethoxyboroxine and a concomitant increase inheat resistant properties. This concentration may be readily increasedto 30 parts of a boroxine such as trimethoxyboroxine per hundred partsof epoxy resin. Not only is the rate of reaction between thetrimethoxyboroxine and epoxy resins inhibited, but the maximum exothermis significantly reduced with the phenyl substituted alkyl alcoholaddition, as shown in FIG. 4.

                  TABLE 1                                                         ______________________________________                                        THE EFFECT OF BENZYL ALCOHOL                                                  ON MAXIMUM EXOTHERM                                                                           Curve                                                                         2     3         4                                             ______________________________________                                        Trimethoxy Boroxine                                                                             10      10        10                                        Benzyl Alcohol    2       3         4                                         Dow DEN-431       85      85        85                                        Neopentyl Glycol  15      15        15                                        Diglycidyl Ether                                                              Gel Time (Minutes)                                                                              65      85        No sharp                                                                      gel time                                  Maximum Exotherm (°F.)                                                                   270     215       155                                       ______________________________________                                    

While phenyl substituted alkyl alcohols permit increased concentrationof the trimethoxyboroxine in the epoxy resin, benzyl alcohol ispreferred. Benzyl alcohol is preferred because of its purity, as well asits index of refraction, its clear color, it high flash point, itsrelatively low solubility in water, its low vixcosity, and its highboiling point.

Both the epoxy resins capable of serving as the matrix for the intenseheat resistant composite and the trimethoxyboroxine and their heatresistant properties are known to those skilled in the art of compositetransparency production. However it is the inclusion of the phenylsubstituted alkyl alcohol which enables one to increase the level oftrimethoxyboroxine which results in an increase in intense heatresistance for the transparency not otherwise present. The phenylsubstituted alkyl alcohol is present in a concentration of from about 20parts to about 50 parts per one hundred parts of trimethoxyboroxine orfrom about 1 parts to about 10 parts per 100 parts of epoxy resin.Preferably, the concentration of benzyl alcohol is 33 parts to onehundred parts of trimethoxyboroxine, or 3.3 parts to one hundred partsof epoxy resin.

Referring now to FIG. 1, it may be seen that the transparency composite,generally referred to as 10, is composed of three layers with the epoxyresin interply 20, a reaction product of an adduct of trimethoxyboroxineand benzyl alcohol with an epoxy resin placed between an inside ply 40and an outside ply 30. The outside ply 30 may be composed of transparentmaterials well known to those skilled in the art and specificallyproviding impact, ballistic, abrasion, weather resistant and lightreflectant resistant properties which resin interply 20 complements.Typically, this outside ply 30 may be composed of acrylic,polycarbonate, polyurethane and any of the silicates commonly known asglass. Likewise, inside ply 40 may be chosen from those same transparentmaterials or others well known to those skilled in the art which are notnecessary for impact, ballistic, abrasion, weather resistant or lightreflection resistance.

All of the components of interply 20 are mixed and degassed, then castagainst an acrylic ply through the use of a casting cell technique wellknown to individuals in the industry. Should it be necessary to castinterply 20 by itself, the same technique can be used, the onlydifference being interply 20 would be cast against a chemically treatedglass plies, such that after cure the glass plies can be removed,resulting in an optically clear interply 20. This interply casting canthen be bonded to other transparent layers with materials as discussedbelow. However, the use of the alcohol permits larger castings thanpreviously possible. Gel times are increased by the addition of thealcohol to permit larger castings, as may be seen in FIG. 3.

When joining the various plies 20, 30, and 40 of the transparencycomposite 10, it may be necessary to use binding means to insureadequate contiguity between the various layers. For example, bindingmeans 45 may exist between the intense heat resistant resin interply 20and inside ply 40, and this binding means 45 may be chosen fromadhesives such as silicones, urethanes and epoxies. Also, binding means35 may be necessary between intense heat resistant resin interply 20 andoutside ply 30, the composition of such binding means being typicallysilicones, urethanes, and epoxies.

However, it is preferred to utilize a mercaptan resin for binding means35 and 45, as described below, to increase resistance to moisturepermeability for transparency composite 10.

The intense heat resistant resin interply 20 may optionally be composedof an epoxy resin cured with adducts of a boroxine such astrimethoxyboroxine, phenyl substituted alkyl alcohols, and organicphosphorus compounds selected from the following group: diphenylphosphite, trisnonylphenyl phosphite, triphenyl phosphite,diphenylisodecyl phosphite, diphenylisooctyl phosphite andphenyldiisodecyl phosphite. Preferably, diphenyl phosphite and triphenylphosphite may be used. The addition of from 20 parts to 400 parts of anorganic phosphorus compound such as per 100 parts of the boroxine suchas trimethoxyboroxine or from about 1 part to about 40 parts per 100parts of the epoxy resin dramatically increases the intense heatresistant properties of the interply 20 at high temperatures, typicallygreater than 2000° F. Alternately, the concentration of the organicphosphorus compound may be from about 50 parts to 250 parts per 100parts of the boroxine or from about 5 parts to about 40 parts per 100parts of the epoxy resin. The addition of this amount of triphenylphosphite provides sufficient phosphorus in the resin to increase thetime of burn-through of a 1/4 inch casting of interply 20 almost tentimes as long as interply 20 without phosphorus at these hightemperatures. The addition of phosphorus is further beneficial byproviding a greater than 20 percent increase in time of burning at thelower temperatures around 2000° F. Therefore, the inclusion of thisphosphite significantly increases the intense heat resistant propertiesalready present in the interlayer 20 and complements the other resistantproperties in outer layer 30 in the transparency composite 10.

Referring now to FIG. 2, the importance of intense heat resistant epoxyresin interply 20 in a clad composite transparency may be understood.This transparency 50 is shown cross-sectionally to demonstrate theeffectiveness of a particular clad composite format. Clad outside ply 30having binding means 35 is secured to intense heat resistant resininterply 20 comprising an epoxy resin cured with adducts oftrimethoxyboroxine and benzyl alcohol alone or together with triphenylphosphite. A silicone interlayer 80 functions as a flexible adhesive tothe opposite surface of interply 20 to a silicate layer 70 typicallycomposed of soda lime glass, borosilicate glass, aluminosilicate glass,silica glass or 96 percent silica glass. On the opposite side ofsilicate layer 70 is an interlayer 60 which consists of a silicone orpolyurethane or polyvinyl butyral interlayer. On the opposite side ofinterlayer 60 is a second silicate layer 70. On the opposite side of thesecond silicate is binding means 45 which consists of a silicone orpolyurethane interlayer. On the opposite side of the binding means 45 isthe inside ply 40 of the composite, composed of the same materials asdiscussed above, including polycarbonate.

However, it is also possible to utilize a mercaptan resin for any or allof binding means 35 and 45 and interlayers 60 and 80. The importance ofsuch mercaptan resin in moisture permeability resistance for composite50 is described below.

It has been found that the combination of these layers 20, 30, 35, 40,45, 60, 70, and 80 in the order described above provides a synergisticresistance greater than the application of layers 30 and 40 surroundinginterlayer 20. Clad outer layer 30 may be selected from thosetransparent materials commonly known to those skilled in the art, asdescribed above and may typically be acrylic.

For an understanding of the improved heat resistant properties ofinterply 20, reference is had to FIG. 5.

                  TABLE 2                                                         ______________________________________                                        HEAT RESISTANCE                                                               TRANSPARENCIES - RELATIONSHIP                                                 BETWEEN BURNTHROUGH TIME AND                                                  EXPOSURE TEMPERATURE                                                                      Line                                                                          A     B        C       D                                          ______________________________________                                        Trimethoxy Boroxine                                                                         7.5     10       10    7.5                                      Benzyl Alcohol                                                                              --      5        3     2.5                                      Triphenyl Phosphite                                                                         --      5        10    --                                       DER-332       100     --       --    --                                       DEN-431       --      85       90    90                                       Heloxy-68     --      15       --    --                                       Silane A-187                                                                  Diphenyl Phosphite                                                                          --      --       --    15                                       Burnthrough at                                                                              378     522      790   9000                                     2000° F. (secs.)                                                       Burnthrough at                                                                              0.4     3.0      3.7   5.8                                      6000° F. (secs.)                                                       ______________________________________                                    

It can be seen from FIG. 5 that by the addition of benzyl alcohol, ahigher concentration of trimethoxyboroxine can be incorporated,resulting in improved, burn-through resistance at 2000° F. and at 6000°F.

Transparencies 10 and 50 which contain interply 10 may be utilized invarious military and industrial applications. Typically, theseapplications may include the use of transparencies in military hardwareand aircraft, as well as spacecraft. Further, industrial applicationsinclude transparencies where protection against the thermal effects offossil fuel fires, thermal nuclear blasts and high energy radiation arerequired.

The lasting success of any transparency composite, designed to withstandhigh heat resistance, impact resistance, ballistic resistance, abrasionresistance, remains dependent upon its continuing transparent nature.The plurality of layers of composites 10 and 50 and the chemicalcomposition of each layer are differentially susceptible to thepermeation of moisture into and through the layers. The retention ofmoisture between and within the various layers of this invention and anyconventional transparency composite having multiple layers creates ahaze which disrupts clarity of light transmissions through thetransparency composite.

A barrier to the generation of haze is necessary for any multi-layertransparency composite. The layers 35 and 45 and interlayers 60 and 80have been found to provide the most effective permeation barrier,resistant to moisture permeability into central layers, such as heatresistant interlayer 20 and silicate layers 70 as seen in FIG. 1 andFIG. 2.

The composition for the binding means 35 and 45 and interlayers 60 and80 comprises about 100 parts by weight of a mercaptan terminated resin,from about 40 to about 250 parts by weight of an epoxy resin anddesirably from about 100 to about 200 parts by weight, and from about0.5 to about 4.0 parts by weight of a silane catalyst.

The mercaptan terminated resin is an aliphatic hydrocarbon basedcompound having a thio reactive group terminating each end of themolecule. The mercaptan has the following general formula: ##STR5##where R is an aliphatic hydrocarbon having from 1 to 18 carbon atoms andn is 1 or 2. The mercaptan resin is a material commercially availablefrom Diamond Shamrock Corporation and sold identified as DION-3-800LC.

The epoxy resin of the binding means 35 or 45 or interlayer 60 or 80 iscomposed of epoxy resins previously disclosed with reference to interply20. Typical epoxy resins include, but are not limited to, bisphenol-Atype, bisphenol-F type, and novolac type epoxy resins. A preferredconcentration of the epoxy resin depends on the type of epoxy resinused. For an epoxy-novolac type resin the preferred concentration isabout 175 parts by weight. For a bisphenol-F type the preferredconcentration is about 100 parts by weight. Epoxy resins commerciallyavailable include DER-332, a product of Dow Chemical Company.

The silane catalyst of the binding means 35 or 45 or interlayer 60 or 80is composed of an am terminated silane compound such as

N-aminoalkyl-aminoalkyl-trialkoxysilanes of the formula ##STR6## whereinR₁ is an alkylene having 1-6 carbon atoms and R₂ is an alkyl, having 1-6carbon atoms, and

aminoalkyl-trialkoxysilanes of the formula ##STR7## wherein R₁ and R₂are as defined above.

Examples of preferred silanes are gamma aminopropyl triethoxy silane andnormal beta aminopropyl gamma aminopropyl trimethoxy silane. Thepreferred concentration of the amino-silane catalyst is about 2.5 partsby weight. The amino-silane is commercially available from Union Carbidein their A-1110 and A-1120 formulations.

As expressed above, the binding means 35 or 45 and interlayer 60 or 80have traditionally employed conventional silicones, urethanes, andepoxies. However, use of the mercaptan interlayer for these purposesprovides unexpected improvement to resistance to moisture permeation.The following table compares the test samples having various compositeconstructions, including a construction having outer ply 30, heatresistant interlayer 20, binding means 45 and inner ply 40, such as thatseen in FIG. 11, and a construction having no binding means 35 or 45.

                  TABLE 3                                                         ______________________________________                                                                      Thick-                                          Composite                     ness                                            Number      Composite Component                                                                             (in.)                                           ______________________________________                                        1           polycarbonate (30)                                                                              0.256                                                       silicone resin (35)                                                                             0.1                                                         Heat resistant interlayer (20)                                                                  0.236                                                       silicone resin (45)                                                                             0.1                                                         polycarbonate (40)                                                                              0.256                                           2           polycarbonate (30)                                                                              0.256                                                       mercaptan interlayer (35)                                                                       0.1                                                         heat resistant interlayer (20)                                                                  0.236                                                       mercaptan interlayer (45)                                                                       0.1                                                         polycarbonate (40)                                                                              0.256                                           3           as-cast acrylic (30)                                                                            0.125                                                       heat resistant interlayer (20)                                                                  0.236                                                       as-cast acrylic (40)                                                                            0.125                                           4           as-cast acrylic (30)                                                                            0.125                                                       heat resistant interlayer                                                                       0.236                                                       silicone resin (45)                                                                             0.1                                                         polycarbonate (40)                                                                              0.256                                           5           as-cast acrylic (30)                                                                            0.125                                                       heat resistant interlayer (20)                                                                  0.236                                                       mercaptan layer (45)                                                                            0.1                                                         polycarbonate (40)                                                                              0.256                                           6           stretched acrylic (30)                                                                          0.1                                                         heat resistant interlayer (20)                                                                  0.125                                                       stretched acrylic (40)                                                                          0.1                                             7           urethane (30)     0.1                                                         heat resistant interlayer (20)                                                                  0.236                                                       urethane (40)     0.1                                             8           urethane (30)     0.1                                                         silicone resin (35)                                                                             0.1                                                         heat resistant interlayer (20)                                                                  0.235                                                       silicone resin (45)                                                                             0.1                                                         urethane (40)     0.1                                             9           urethane (30)     0.1                                                         mercaptan interlayer (35)                                                                       0.1                                                         heat resistant interlayer (20)                                                                  0.236                                                       mercaptan interlayer (45)                                                                       0.1                                                         urethane (40)     0.1                                             10          as-cast acrylic (30)                                                                            0.08                                                        heat resistant interlayer (20)                                                                  0.236                                                       as-cast acrylic (40)                                                                            0.08                                            11          as-cast acrylic (30)                                                                            0.1                                                         silicone resin (35)                                                                             0.1                                                         heat resistant interlayer (20)                                                                  0.236                                                       silicone resin (45)                                                                             0.1                                                         as-cast acrylic (40)                                                                            0.1                                             12          as-cast acrylic (30)                                                                            0.08                                                        mercaptan interlayer (35)                                                                       0.1                                                         heat resistant interlayer (20)                                                                  0.236                                                       mercaptan interlayer (45)                                                                       0.1                                                         as-cast acrylic (40)                                                                            0.08                                            ______________________________________                                    

The composites of TABLE 3 were tested under extreme temperature andhumidity conditions. The direct comparison of the performance of themercaptan resin of the present invention and the performance of theconventional silicone resin, or no binding means at all, may be seen inthe graphs of FIGS. 6-9.

In FIG. 6, the percent of haze occurring in the composite is comparedwith days of constant exposure of the composite at 200° F. and 100percent relative humidity. All other parameters constant, a directcomparison of composite No. 1 with conventional silicone resin andcomposite No. 2 with the mercaptan interlayer of the present inventiondemonstrates the increased resistance to moisture permeation in thelatter composite. Likewise, a direct comparison of composites No. 4 andNo. 5 show the increased resistance to moisture permeation in the lattercomposite. Composites No. 2 and No. 5 are clearly superior to theircounterparts No. 1 and No. 4, as well as No. 3 and No. 6 which do notprovide any binding means moisture permeation protection.

In FIG. 7, a graph showing the effect of constant exposure to 120° F.and 95 percent relative humidity to the same six composites is seen.While not as pronounced as that seen in FIG. 6, the comparison ofcomposites No. 1 and No. 2 and of composites No. 4 and No. 5 clearlyindicates the superiority of the mercaptan interlayer binding means overthe silicone resin binding means.

In FIG. 8, the graph showing the test of exposure at 200° F. and 100percent relative humidity for the remaining six composites is seen. Adirect comparison of composites No. 8 and No. 9, where the onlydifference is the substitution of mercaptan interlayer for siliconeresin, demonstrates the clear superiority of the mercaptan resin inresistance to haze as caused by moisture permeation. Further, acomparison of composites No. 11 and No. 12, substituting mercaptaninterlayer for silicone resin, demonstrates the superiority of themercaptan interlayer of the present invention over conventional bindingmeans.

FIG. 9 summarizes the superiority of the mercaptan interlayer of thepresent invention over conventional or no resin by comparing performanceat 200° F./100% relative humidity with performance at 120° F./95%relative humidity. At identical acceptable percentage haze levels, themercaptan interlayer could last as long as 100 days at 120° F./95%relative humidity and 35 days at 200° F./100% relative humidity. Bycomparison, the silicone resin could only withstand about 22 days at120° F./95% relative humidity and 8 days at 200° F./100% relativehumidity.

FIGS. 6-8 also demonstrate that the mercaptan interlayer of the presentinvention is effective for conventional outer and inner plies 30 and 40:acrylic, polycarbonate, urethane, and any combinations of them.Moreover, the mercaptan interlayer is available to replace theconventional silicone, epoxy, or urethane resins for any transparencycomposite using any conventional transparency including silicatescommonly known as glass. Indeed, the mercaptan interlayer of the presentinvention is an effective interlayer 60 and 80 for clad compositetranspraency 50 as seen in FIG. 2.

Table 4 below demonstrates a comparison of the specific permeabilityvalues for various formulations of the mercaptan interlayer andconventional silicone and other resins. The specific permeability of afilm to moisture is defined as the milligrams of water that permeate onesquare centimeter of film of 1 millimeter thickness each 24 hours aftera constant rate has been attained under the preferred conditions of 25°C. and using 100% relative humidity inside the cup and a phosphoruspentoxide desiccated atmosphere outside the cup. The formula ofcalculation is ##EQU1## where SP is specific permeability, W is weightloss in milligrams in a 24 hour period, T is the film thickness ininches, and A is exposed cup surface area.

                  TABLE 4                                                         ______________________________________                                                         Film    Specific                                                              Thick-  Permeability.sup.4                                   Type Of Resin    ness    (ASTM D-1632-62)                                     ______________________________________                                        mercaptan interlayer.sup.1                                                                     0.098   0.4978                                               mercaptan interlayer.sup.2                                                                     0.124   0.0627                                               mercaptan interlayer.sup.3                                                                     0.114   0.4633                                               low-strength silicone                                                                          0.100   4.8539                                               low-strength RTV sili-                                                                         0.104   4.2270                                               cone                                                                          high-strength silicone                                                                         0.100   4.8768                                               high-strength RTV sili-                                                                        0.118   5.4549                                               cone                                                                          pigmented RTV silicone                                                                         0.101   4.0020                                               ______________________________________                                         .sup.1 Mercaptan interlayer comprising 100 parts by weight of mercaptan       resin, 100 parts by weight of epoxy resin, and 2 parts by weight of silan     catalyst.                                                                     .sup.2 Mercaptan interlayer comprising 100 parts by weight of mercaptan       resin, 50 parts by weight of epoxy resin, and 1.5 parts by weight of          aminosilane catalyst.                                                         .sup.3 Mercaptan interlayer comprising 100 parts by weight of mercaptan       resin, 100 parts by weight of epoxy resin, and 1 part by weight of            aminosilane catalyst.                                                         .sup.4 Units in mg. · mm/24 hr. cm.sup.2.                       

Because the ideal specific permeability is near zero, it is readily seenthat a mercaptan interlayer of the present invention is approximately 10times better than conventional resins. This direct comparisondemonstrates the vast superiority of a mercaptan interlayer of thepresent invention over those binding agents presently employed.

Two other properties significant for the interlayer of the presentinvention are ultimate strength and modulus. During high temperature,high humidity condition, the interlayer must maintain proper adhesion toprevent delamination of the interlayer and the other various layers inthe composite. Further, the interlayer must have an acceptable rate ofchange of modulus during the high temperature, high humidity conditions,to prevent alteration of the interlayer effectiveness sandwiched betweenother layers during the course of use. For a comparison of modulus andultimate strength properties of the interlayers of the present inventionwith interlayers common to those skilled in the art, reference is had toTables 5 and 6. Table 5 describes the formulation of the testingmaterial and Table 6 demonstrates the effect of high temperature andhigh humidity on the modulus and ultimate strength properties of theformulations.

                  TABLE 5                                                         ______________________________________                                        FORMULATION OF INTERLAYER FOR COMPOSITE                                       OF GLASS - INTERLAYER - POLY CARBONATE                                               Mercap-                 High   Fumed                                   Formu- tan      Epoxy   Amino- Strength                                                                             Silica                                  lation Resin    Resin   Silane Silicone                                                                             Compound 1                              ______________________________________                                        1      100      100     2      --     --                                      2      100      150     2      --     --                                      3      100      175     2      --     --                                      4      100      200     3      --     --                                      5      --       --      --     100    5                                       6      --       --      --     100    --                                      ______________________________________                                         *1 A thixotropic agent available commercially as CABO-SIL EH5.           

                                      TABLE 6                                     __________________________________________________________________________    Torsional - Shear Modulus/Ultimate                                            Strength (PSI)                                                                          Formulation                                                                   1    2   3    4    5   6                                            __________________________________________________________________________    Days of                                                                              1  210/771                                                                            78/148                                                                            25/62                                                                              28/60                                                                              25/43*                                                                            16/53                                        Exposure at                                                                          2  207/450                                                                            --  22   22    6/8**                                                                            --                                           120° F./95%                                                                   3  --   --  --   --   --  22/72                                        Relative                                                                             4  --   --  --   --   --    7/19**                                     Humidity                                                                             6  190/291                                                                            49/110                                                                            --   33/67                                                                              6/10                                                                              --                                                  7  --   --  33/65                                                                              --   --  --                                                  14 166/266                                                                            73/122                                                                            --    98/153                                                                            9/14                                                                              --                                                  15 --   --   55/101                                                                            --   --  --                                                  27  85/200                                                                            --  --   105/289                                                                            --  --                                           __________________________________________________________________________     *Haze Appeared                                                                **Delamination Started                                                   

As may be seen from an examination of Table 6, a variation in theformulation of the inner layer of the present invention may control themodulus and its rate of change during the days of exposure tohigh-temperature/high-humidity conditions. Over the course of the periodexamined, the ultimate strength and its rate of change could becontrolled by the type of formulation of the interlayer. Generally, withincreasing epoxy resin concentration, the modulus and ultimate strengthcomparisons during the days of the exposure increased when the epoxy wasgreater than 150 parts per 100 parts of mercaptan resin.

Table 6 also demonstrates the clear superiority of the interlayerformulations of the present invention over those interlayer compositionsknown to those skilled in the art. On the first day, formulation No. 5exhibited haze, and by the fourth day, both silicone formulationsstarted to delaminate from the composite ofglass-interlayer-polycarbonate. In comparison to this, the formulations1 and 4 lasted as long as 27 days when the experiment was concluded toreport these results. Furthermore, the interlayer formulations of thepresent invention have a variety of modulus and ultimate strengthproperties to meet various commercial applications depending upon thematerials between which the interlayer is sandwiched.

From an examination of FIGS. 13 and 14, it is possible to optimize theformulation for modulus stability and ultimate strength stability. FIG.13 demonstrates in graphic form the information shown in Table 6 for acomparison of initial modulus with the modulus after 14 days ofexposure. A ratio of epoxy resin/mercaptan resin exhibits stability overthe 14 days in the range of 1.5 to 1.8. Likewise, this ratio isconfirmed for ultimate strength comparisons as seen in FIG. 14.

The mercaptan composition of the present invention is effective, notonly to resist moisture permeation between plies of transparentcomposite construction. As seen in FIG. 10, edge sealant 95 may sealedges of outer ply 30, heat resistant interlayer 20, binding means 45(either of the invented composition or a conventional composition) andthe upper surface of inner layer 40. The composite shown in FIG. 10 isthe same as the composite 90 shown in FIG. 11, typical of transparentcomposites used in high elevation aircraft. Edge sealer 95 is likewiseuseful to seal edges of composites 20 and 50 shown in FIG. 2 or anyconventional transparent composite, either with inner ply 40 extendingbeyond the other transparency components or cut at the same place as theother transparency components.

The mercaptan composition may also fill in the slot created curing themanufacture of the transparency on the outside edge of any transparencycomposite. As seen in FIG. 12, this slot filler 105 combines thefunctions of the edge sealant 95 and the interlayer 45. Neither the slotfiller 105 nor the edge sealant need be transparent and may betranslucent or opaque with the addition of thixotropic agents, such asfumed silica compounds, or fillers. Indeed, slot filler 105 and edgesealer 95 may merge into a perimeter sealant.

The edge sealer 95 and the slot filler 105 demonstrates significantimprovements over the use of high-strength silicones known to thoseskilled in the art. An examination of Table 7 demonstrates the moistureimpermeability of the mercaptan compositions over that of thehigh-strength silicone.

                                      TABLE 7                                     __________________________________________________________________________    EXAMINATION OF GLASS-SILICONE-POLYCARBONATE                                   COMPOSITES WITH EDGE SEALERS AND SLOT FILLERS                                 EXPOSED 29 DAYS AT 120° F./95% R.H.                                               PANEL NO. 1                                                                           PANEL NO. 2                                                                              PANEL NO. 3                                                                              PANEL NO. 4                                                                              PANEL NO.                 __________________________________________________________________________                                                        5                         SLOT-FILLER                                                                              HIGH-STRENGTH SILICONE        MERCAPTAN* MERCAPTAN**               (105)      PLUS 5% BY WT.                COMPOSITION                                                                              COMPOSITION                          CAB-O-SIL EH-5                PLUS 5% BY WT.                                                                           PLUS 5% BY WT.                       (Fumed Silica Compound)       CAB-O-SIL EH-5                                                                           CAB-O-SIL EH-5                                                     (Fumed Silica                                                                            (Fumed Silica                                                      Compound)  Compound)                 EDGE-SEALER                                                                              NONE    MERCAPTAN  MERCAPTAN  MERCAPTAN  MERCAPTAN                 (95)               COMPOSITION*                                                                             COMPOSITION**                                                                            COMPOSITION*                                                                             COMPOSITION**                                PLUS 5% BY WT.                                                                           PLUS 5% BY WT.                                                                           PLUS 5% BY WT.                                                                           PLUS 5% BY WT.                               CAB-O-SIL EH-5                                                                           CAB-O-SIL EH-5                                                                           CAB-O-SIL EH-5                                                                           CAB-O-SIL EH-5                               (Fumed Silica                                                                            (Fumed Silica                                                                            (Fumed Silica                                                                            (Fumed Silica                                Compound)  Compound)  Compound)  Compound)                 INTERLAYER Slot-Filler                                                                           Edge sealer cut                                                                          Edge sealer cut                                                                          Edge sealer cut                                                                          Edge sealer cut           (HIGH-STRENGTH                                                                           can be removed                                                                        off        off        off        off                       SILICONE)  Silicone inter-                                                                       Slot-Filler could                                                                        Slot-Filler could                                                                        Slot-Filler                                                                              Slot-Filler had           (45)       layer can be                                                                          be removed with                                                                          be removed with                                                                          could be removed                                                                         to be dug out                        readily delam-                                                                        manual difficulty                                                                        difficulty with difficulty                                                                          Silicone inter-                      inated from                                                                           Silicone inter-                                                                          Silicone inter-                                                                          Silicone inter-                                                                          layer appeared                       glass and poly-                                                                       layer could be                                                                           layer could be                                                                           layer appeared                                                                           to be well                           carbonate                                                                             delaminated from                                                                         delaminated from                                                                         to be well bonded - minor                               both. The adhe-                                                                          glass only - was                                                                         bonded     spot delamina-                               sion was much                                                                            better than           tions                                        better than Panel                                                                        Panel No. 1                                                        No. 1                                                              *Mercaptan Resin 100       **Mercaptan Resin                                                                              100                                Epoxy Resin     100        Epoxy Resin     200                                Amino-Silane    2          Amino-Silane    2                         __________________________________________________________________________

Each panel was subjected to 29 days of exposure at 120° F. and 95%relative humidity. Panel No. 1 only had a high-strength silicone slotfiller and once that was removed, it was apparent that the siliconeinterlayer could be readily delaminated from both the glass and thepolycarbonate layers. In contrast to this the mere addition of an edgesealer having one mercaptan composition plus the thixatropic agentincrease the performance of the composite during the 29 days ofexposure. After the edge sealer 95 was cut off, the slot filler 105could only be removed with manual difficulty. However, the siliconeinterlayer could be delaminated from both the glass and polycarbonate,although the adhesion was better than that found in Panel 1. Byincreasing the epoxy resin concentration of the mercaptan composition,Panel 3 demonstrated some improvement over that seen for Panel 2. Inthis case, after the edge sealer and slot filler were cut off andremoved with manual difficulty, the silicone interlayer could bedelaminated from only the glass layer. While Panels 2 and 3 representimprovement over the conventional performance of Panel 1, Panels 4 and 5provide even greater improvement.

By using the mercaptan compositions for both slot filler 105 and edgesealer 95, the interlayer was significantly protected from moisturepermeation. For the interlayers of Panels 4 and 5, the combination ofthe edge sealer and slot filler provided the protection to maintain abond between the silicone interlayer and both the glass andpolycarbonate. Indeed, using this second mercaptan composition, slotfiller 105 had to be dug from the periphery of the Panel No. 5.

The mercaptan compositions of the present invention not only serve as aninterlayer, but also may serve as an edge sealer or slot filler. Thevariety of combinations of transparent composites which may employ thecomposition of the present invention in these various functions iswithin the scope of this invention.

While in accordance with the Patent Statutes, one best mode andpreferred embodiment of the invention has been provided, the inventionis not to be limited thereto or thereby. Therefore, for an understandingof the scope of the invention, reference is had to the following claims.

What is claimed is:
 1. A transparent composition having resistance tointense heat, comprising:(a) a transparent blend having from about 80parts to about 100 parts by weight of an epoxy resin; (b) from about 5to about 30 parts by weight of a boroxine having the formula: ##STR8##where R is a group having from 2 to 18 carbon atoms; and (c) from 1 partto about 10 parts by weight of a phenyl substituted alkyl alcohol; saidalkyl alcohol having from 1 to 20 carbon atoms.
 2. A transparentcomposition having resistance to intense heat, according to claim 1,wherein R, of said boroxine is an alkyl group having from 2 to 5 carbonatoms; wherein said alkyl alcohol has from 1 to 10 carbon atoms, andwherein said amount of said boroxine is from about 7.5 to about 30 partsby weight.
 3. A transparent composition having resistance to intenseheat, according to claim 2, wherein said boroxine comprises about 10parts by weight and; wherein said phenyl substituted alkyl alcohol isbenzyl alcohol and wherein said alcohol comprises about 3 parts byweight.
 4. A transparent composition having resistance to intense heat,according to claim 1, wherein said transparent blend further comprisesfrom about 1 part to about 40 parts by weight of a phosphite selectedfrom the group consisting of diphenyl phosphite, trisnonylphenylphosphite, triphenyl phosphite, diphenylisooctyl phosphite,phenyldiisodecyl phosphite, diphenylisodecyl phosphite, and combinationsthereof.
 5. A transparent composition having resistance to intense heat,according to claim 2, wherein said transparent blend further comprisesfrom about 1 part to about 40 parts by weight of a phosphite compound.6. A transparent composition having resistance to intense heat,according to claim 2, including from about 5 to about 40 parts by weightof a phosphite selected from the group consisting of diphenyl phosphite,trisnonylphenyl phosphite, triphenyl phosphite, diphenylisooctylphosphite, phenyldiisodecyl phosphite, diphenylisodecyl phosphite, andcombinations thereof.
 7. A transparent composition having resistance tointense heat according to claim 6, wherein said phosphite is triphenylphosphite.
 8. A transparent composition having resistance to intenseheat according to claim 3, including from about 5 to about 40 parts byweight of triphenyl phosphite.